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Adding Precise Wave-Propagation Information and Geodetic Corrections to Standard SAR Products M. Eineder1,3, U. Balss1, X. Cong3, S. Suchandt1, C. Gisinger2, H. Runge1
1Remote Sensing Technology Institute (IMF), German Aerospace Center (DLR) 2Institute for Astronomical and Physical Geodesy (IAPG), Technische Universität München (TUM), 3Chair of Remote Sensing Technology (LMF), Technische Universität München (TUM)
CEOS SAR Calibration and Validation Workshop, ESA ESTEC 2015
DLR.de • Chart 2 > CEOS SAR Cal/Val 2015 > M. Eineder > Geodetic SAR Product > 28.10.2015
Point Positioning Accuracy: SAR versus GNSS
GPS (90’s)
SNR=26 dB (20 ms) B=1 MHz (10 MHz)
SCR=5-40 dB B=150 MHz
DLR.de • Chart 3 > CEOS SAR Cal/Val 2015 > M. Eineder > Geodetic SAR Product > 28.10.2015
Yes, it is Possible to Localize Objects with cm Accuracy
Literature: 1) Eineder, M., Minet, C., Steigenberger, P., Cong, X., Fritz, T.,
Imaging Geodesy—Toward Centimeter-Level Ranging Accuracy With TerraSAR-X. IEEE TGRS, 2011
2) Schubert, A., Jehle., M., Small, D., Meier, E., Mitigation of atmospheric perturbations and solid-Earth movements in a TerraSAR-X time-series, J. of Geodesy, 86(4), 2012.
3) Cong, X., Balss, U., Eineder, M., Fritz, T., Imaging Geodesy—Centimeter-Level Ranging Accuracy With TerraSAR-X: An Update. IEEE GRSL, 2012
4) Gisinger, C., Balss, U., Pail, R., Zhu, X.X., Montazeri, S., Gernhardt, S., Eineder, M., Precise Three-Dimensional Stereo Localization of Corner Reflectors and Persistent Scatterers With TerraSAR-X. IEEE TGRS, 2015
5) Schubert, A., Small, D., Miranda, N., Geudtner, D., Meier, E., Sentinel-1A Product Geolocation Accuracy: Commissioning Phase Results, Remote Sens, 2015
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range offset [m] TSX (34°…
… but not yet for everybody and everywhere!
Local TSX positioning accuracy of a CR, corrected for solid earth tides, atmospheric refraction (H2O, TEC), pole tides etc.
σ=10.8 mm
σ=13
.0 m
m
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Design goals: • Improve positioning of SAR image data • As accurate as possible / foreseeable: mm-level • Not to impact data integrity • Usable for InSAR phase corrections • Easy to use for scientists & SW developers
Challenges:
• Projection: 3D2D • Height dependency
Decision: Not: interpolation of SAR image data But: correction layer in time coordinate system
Geodetic SAR Product: Goals & Challenges
Troposphere 18 km
Ionosphere 50-1000 km SAR Satellite
θ
Earth Dynamics (e.g. ETRF) 0
1 ( )2 2cR R c t dt
ττ= → = ∫
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SAR Geodetic Processor Architecture & Flow Chart
SAR Processor (TMSP)
Annotation
SAR Geodetic Processor (TMSP)
SSC
Corr. Grids
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Geodetic SAR Product Design: Correction Layer
y0, x0
y0, x1
y0, x2
..
.. y0, xn-1
y1, x0
y1, x1
y1, x2
..
.. y1, xn-1
y2, x0
y2, x1
y2, x2
..
.. y2, xn-1
..
.. .. ..
..
.. .. ..
..
..
ym-1, x0
ym-1, x1
ym-1, x2
..
.. ym-1, xn-1
y
x ρx
ρy
• (x,y): Point coordinates in radar & map projection
• G (x,y): Regular grid w.r.t. (x,y)
• ρx, ρy: Grid resolution 200 – 1000 m
G(x,y)
Annotations per Grid Cell: Base Parameters
t Slow time (UTC)
τ Fast time
λ,ϕ,h Geographic coord. (WGS84)
x,y,z x,y,z coordinates in ITRF
a, r image pixel coordinates
los Line-of-sight vector in ITRF
ϑ local incidence angle
hsat Platform elevation
∆tsum Sum of slow time corrections
∆τsum Sum of fast time corrections
Atmospheric Corrections
∆ttropo Slow time correction (0.0)
∆τtropo Fast time correction
∆’τtropo d∆τtropo/d∆h for assumed height h
Ionospheric Corrections
∆tion Slow time correction (0.0)
∆τion Fast time correction
Spares for Future Corrections
∆tOL Slow time correction, ocean load
∆τOL Fast time correction, ocean load
∆xOL delta-x in ITRF, ocean load
∆yOL delta-y in ITRF, ocean load
∆zOL delta-z in ITRF, ocean load
:
Solid Earth Tide Corrections
∆tSET Slow time correction
∆τSET Fast time correction
∆xSET delta-x
∆ySET delta-y
∆zSET delta-z
∆λ latitude correction
∆ϕ latitude correction
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• Geodynamic effects: • IERS Conventions for solid earth tides (GNSS compatible) • Coordinate transforms (e.g. ITRF-ETRF)
• Tropospheric delays:
• 4D ECMWF ERA-Interim data; 80 km res, 60 vertical levels, 1/(6 hours)
• Ionosphere: • CODE (Center for Orbit Determination Europe) Uni Bern • DLR Space Weather Applications Center (SWACI)
Data Sources for Correction Layer
DLR.de • Chart 8 > CEOS SAR Cal/Val 2015 > M. Eineder > Geodetic SAR Product > 28.10.2015
Example: Solid Earth Tides - IERS Conventions
Global map of geometric surface shifts caused by solid Earth tides on December 6th, 2014, 12:00:00 UTC (full moon).
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SAR Geodetic Product Product Example
Tropspheric range correction (ECMWF)
Ionosphericm range correction (CODE)
Geodynamic range correction (IERS)
+ +
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• Example 1: precise geocoding • For every sample (t, τ)
• Read correction values ∆t(t, τ), ∆τ(t, τ) from grid; interpolate • Zero-Doppler geocoding of pixel with timing (t+∆t, τ+∆τ)
• Example 2: InSAR phase correction
• For every sample (t, τ) • Read correction values ∆τmaster(t, τ) and ∆τslave(t, τ) from grid;
interpolate • Correct InSAR phase by 2π(∆τmaster(t, τ)-∆τslave(t, τ))/λ • Optional: apply differential phase correction from high resolution DEM
Recipe
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Example: Removal of Stratified Troposphere
Test Site: Hierro
Master acquisition 2013-04-23T07:15:32
Slave acquisition 2011-11-10T07:15:31
Incidence angle 33°
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Validation with local GNSS Test & validation of tropospheric and ionospheric delays with GNSS measured delays for the Wettzell testsite during TerraSAR-X data takes (radar slant range projected).
Parameter Component Difference
Troposphere (ECMWF – local GNSS) Range 9.9 ± 13.0 mm
Ionosphere (CODE – local GNSS) Range 2.5 ± 2.8 mm
Globally available corrections are only 13 mm worse than local GNSS measurements
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Validation of ECMF Zenith Path Delay IGS Network
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Application: 3D Coordinates from TerraSAR-X Stereo
Lantern
DLR/HGF-Project DriveMark®
DLR.de • Chart 15 > CEOS SAR Cal/Val 2015 > M. Eineder > Geodetic SAR Product > 28.10.2015
Application: 3D Coordinates from TerraSAR-X Stereo
Lantern
Height: +0,96 cm
East: +2,87 cm North: -2,62 cm
105 images
Height: +0,74 cm
East: +3,05 cm
North: +1,46 cm
108 images
DLR/HGF-Project DriveMark®
DLR.de • Chart 16 > CEOS SAR Cal/Val 2015 > M. Eineder > Geodetic SAR Product > 28.10.2015
Application to Sentinel-1 Data: Mexico City Troposphere Ionosphere
Solid Earth Tides
F. Rodriguez, DLR-IMF
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Application to Sentinel-1 Data: Mexico City
Original DInSAR SGP corrections applied
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• New, easy to use realization of a geodetic SAR product demonstrated
• Manifold applications
• Product layer must tightly fit to a(n accurate) SAR processor
• Further study with Sentinel-1
recommended
• Discussion expected
Conclusions
Acknowledgement: project partly funded by the German HGF projects DLR@Uni and Drivemark™